The present invention relates to a collet lifting mechanism for a die handling unit of a die bonder.
Conventionally, in a die bonding process in which a pellet is bonded to a frame, a collet lifting mechanism shown in FIG. 4 is used. The collet lifting mechanism comprises a driven table 1 which is moved upward and downward by a force applied from the outside, a collet 3 connected to the driven table 1 through a spring 2, and a holding guide pate 4 which is attached to the driving table 1 to guide the vertical movement of the collet 3.
When a die bonding is to be performed by this collet lifting mechanism, a pellet 5 is adhered to the lower end of the collet 3, and the driven table 1 is downward moved. This downward movement causes the collet 3 connected to the table through the spring 3 to move downward, and then the pellet 5 adhered to the lower end reaches a surface of a frame 6 on which an adhesive 7 is applied. When the driven table 1 is moved further downward moved, the spring 2 stretches upward because the lower end of the collet 3 has already( reached the frame 6, and the pellet 5 is pressed by the restoring force of the spring against the frame 6 and fixed thereto by the adhesive 7.
In the above-described prior art collet lifting mechanism, since the lower end of the collet is pressed against a frame or the like by a spring force, the load is determined by the spring constant. Hence, such a mechanism has a problem in that owing to variations in thickness of pellets and frames, the bonding load is not constant so that it is impossible to perform a precise die bonding.